Interpretive Summary: Some fungi live entirely within a host plant and can harm the physiology and behavior of grazing livestock that consume the plant – fungus association. The association is very specific, but new technologies have allowed introduction of certain fungal strains into productive tall fescue plant hosts that do not cause detrimental effects in grazing livestock. Fungal infection often benefits productivity and persistence of the host plant, but the influence of novel associations on host productivity and persistence is unclear. We conducted laboratory and field experiments to determine how tall fescue allocated resources among plant parts and how plants that were clipped repeatedly grew in either full sun or shade. The host plants had a native or a novel fungus, or were non-infected. Plants hosting the novel fungus were the smallest among the host – fungus associations; however, these plants produced more shoots than roots compared to plants infected with the native fungus or those that were non-infected. Smaller juvenile plant root systems could influence which plants survive and ultimately impact the productivity, composition, and nutritional value of a pasture over the long term. Shade-grown tall fescue plants were smaller than those growing in full sun. The influence of host-fungus association and site conditions could interact to influence production and persistence of a plant stand. Once established, tall fescue grown in shaded sites should not be grazed as intensively as those in unshaded pasture sites.

Technical Abstract:
Tall fescue (Festuca arundinacea Schreb.) often benefits in terms of productivity and persistence when infected with Neotyphodium coenophialum [Morgan-Jones and Gams], Glenn, Bacon, and Hanlin) endophyte, but the influence of novel non-ergogenic endophytes on these are unclear. We conducted a field experiment using container-grown tall fescue plants to determine how plants allocated resources when clipped repeatedly in microsites differing in the amount of available light associated with open (full sun), and partially shaded (about 20% or 40% of full sun) conditions. Plants of the same tall fescue cultivar (Jesup) were host to either a native or novel non-ergogenic fungal endophyte (Max-Q™), or were devoid of endophyte. Seedlings of plants infected with the novel endophyte had slower germination, germinated later, and allocated more photosynthate to shoots than roots, when compared to J- or J + plants. Herbage production of undisturbed canopies was not influenced by host-endophyte association within a microsite, with more herbage produced at the open than at the heavily shaded site. Clipping plants to a 5- or a 10-cm residue height tended to accentuate differences, with diminished productivity and greater variability occurring when plants were maintained at 5-cm. This trend was supported by allometric resource allocation patterns, and in terms of vegetative propagule mass relative to the number of propagules. Tall fescue, irrespective of host-endophyte association, grown as forage in silvopastoral situations should be managed to maintain no less than a 10-cm residual plant height. Trends in photosynthate allocation and plant size might influence persistence and should be investigated over a longer time interval.